In recent years, in order to improve luminous efficiency in a semiconductor light emitting device such as an organic EL device, fluorescent product and LED, improvements have been studied in light extraction efficiency from the semiconductor light emitting device. Such a semiconductor light emitting device has a configuration that a high refractive index region is sandwiched between low refractive index regions and that a light emitting portion is included inside the high refractive index region. Therefore, emitted light emitted in the light emitting portion becomes a waveguide mode that the light is guided inside the high refractive index region, while being enclosed inside the high refractive index region, and is absorbed in the waveguide process to attenuate. Accordingly, it is not possible to extract the light to the outside of the semiconductor light emitting device, and light extraction efficiency significantly decreases.
In order to effectively improve light extraction efficiency, it is necessary to break the waveguide mode early. Therefore, to improve light extraction efficiency, such a method is proposed that an intermediate refractive index layer is formed between the low refractive index region and the high refractive index region (for example, see Patent Document 1). However, in this method as described in Patent Document 1, it is not possible to break total reflection of light in the interface between the high refractive index region and the intermediate refractive index layer and in the interface between the intermediate refractive index layer and the low refractive index region. Therefore, the totally reflected light maintains the waveguide mode to attenuate, and it is not expected to significantly improve light extraction efficiency.
Further, such a method is proposed that light enclosed by the waveguide mode is extracted as diffracted light using a diffraction grating or zone plate provided in a position for suppressing total reflection in the device interface (for example, see Patent Document 2). In the method as described in Patent Document 2, since required are materials with a refractive index close to that of the high refractive index region and the waveguide mode is broken with diffracted light, light extraction efficiency is improved in only light of a critical angle or more, and it is not expected to obtain radical improvements in light extraction efficiency. Further, glare occurs based on a diffraction color specific to diffracted light. In other words, when a user of a light emitting device sees the light emitting device that is emitting, the user feels glare, visibility to the light emitting device decreases, and softness of light like natural light decreases.
Further, to break the waveguide mode with diffracted light, the diffraction angle dependence for each wavelength is remarkable, and another problems also arises that an emitted light color is seen differently corresponding to an angle to visually identify i.e. so-called the color shift increases.
On the other hand, as another example of breaking the waveguide mode and improving light extraction efficiency, a light extraction film is proposed to extract an evanescent wave oozing from the high refractive index region to the low refractive index region (for example, Patent Document 3). In the light extraction film as described in Patent Document 3, a structuring layer having a first refractive index is provided on a flexible substrate, and a filling material layer containing a material having a second refractive index is provided on the structuring layer. The filling material layer is provided to fill a concavo-convex structure provided on the surface of the structuring layer and to flatten the surface on the side opposite to the structuring layer. In the film for light extraction as described in Patent Document 3, it is designed that when the surface of the filling material layer having the second refractive index comes into contact with the high refractive index region of the light emitting device, the concavo-convex structure of the structuring layer having the first refractive index is included inside the evanescent wave region. Therefore, it is possible to extract the evanescent wave, which occurs in the interface between the filling material layer and the high refractive index region of the waveguide mode light that is reflected in the high refractive index region and returns to the inside of the light emitting device, with the structuring layer, and it is thereby possible to improve light extraction efficiency.
Further, as still another example of breaking the waveguide mode and improving light extraction efficiency, a surface light emitting apparatus is proposed in which a plurality of dielectric antennas is provided on the surface of a light transmission layer provided on the light emitting portion surface (for example, see Patent Document 4).